Optical and antibacterial properties of nickel oxide (NiO) nanoparticles: Effect of annealing temperature

This article describes the influence of annealing temperature on the optical and antibacterial properties of NiO nanoparticles synthesized through a chemical co-precipitation method. The differences in their optical and antibacterial properties were examined. XRD patterns confirm the development of β-Ni(OH) 2 phase and NiO phase. At higher annealing temperature, the phase change from β-Ni(OH) 2 phase to NiO phase is noticed. SEM and TEM images showed the formation of irregular shaped particles, as well as the variation of agglomeration rate with annealing temperature. The decreases of surface area with an increasing annealing temperature because of the agglomeration, which alters the surface reactivity of materials. EDX spectra validated the materials' elemental composition. FTIR spectra show the peaks ranging from 440 cm −1 to 600 cm −1 , confirming the formation of β-Ni(OH) 2 and NiO phases. From UV–Vis absorption analysis, the red shift of absorption edge and the decrease of band gap (4.29 eV–3.67 eV) with an increasing annealing temperature is noticed. The samples antibacterial activity against two pathogens ( S,aureus and E.Coli) was tested using the well-diffusion technique. The diameter of inhibition zone decreases with an increasing annealing temperature due to the increase in the crystallite size and the variation of surface active sites such as oxygen vacancies and Ni 2+ ions. These results indicate that the crystallite size and surface active sites of the NiO nanoparticles are crucial for optical and antibacterial properties. • Synthesis of NiO nanoparticles via a chemical co-precipitation method. • The XRD spectra show the development of β-Ni(OH) 2 phase and NiO phase. • The morphological analysis confirms the formation of irregularly shaped particles. • The band gap of NiO nanoparticles decreases with the annealing temperature. • The antibacterial activity of the samples reduces as annealing temperature increases.